1. Field of Invention
This invention relates to antennas. Specifically, the present invention relates to transceivers for active array antennas.
2. Description of the Related Art
Active array radar systems are employed in various demanding applications including missile target tracking, air traffic control, aircraft guidance, and ground mapping systems. Such applications demand reliable, efficient, and cost-effective radar systems that accurately detect and track targets.
To enhance target detection and tracking accuracy, radar systems often employ high-frequency microwaves or millimeter waves. However, millimeter waves or high-frequency microwaves may cause excessive signal losses, especially in antenna element waveguide feeds. These losses may reduce the overall target detection and tracking capability of the accompanying radar system.
Small millimeter waves require relatively complex active arrays with small components and close component spacing. Waveguides employed to feed the antenna arrays elements are bulky relative to the small active antenna array elements. This places undesirable design constraints on the active array radar system.
Conventionally, active arrays are steered by beam-pointing techniques that involve selective phase shifting of signals fed to the array. These techniques often require a phase shifter at every active array element. Unfortunately, the phase shifters are often lossy and bulky relative to the small millimeter wave antenna elements. Bulky phase shifters at every element place undesirable design constraints on the antenna arrays.
Alternatively, serpentine radio frequency waveguide feeds are employed instead of the phase shifters. Desired phase shifts are achieved by placing taps at strategic positions in the serpentine feed. Radiation from the different taps has different phase depending on tap spacing and input frequency. Unfortunately, these serpentine feeds are also undesirably complex, bulky, and lossy. Furthermore, conventional radar systems employing serpentine feeds and/or phase shifters may require separate sets of transmit/receive modules to scan or steer the radar antenna in both azimuth and elevation. The extra transmit/receive modules are bulky, expensive, and impose additional radar design constraints.
Hence, a need exists in the art for an efficient active array radar design that obviates the need for bulky and lossy antenna feeds and phase shifters. There exists a further need for an active array radar that can be scanned in azimuth and elevation with the same set of transmit/receive modules and without requiring conventional phase shifters.